Constant Phase Element Research Articles

Microrna Detection by Electrochemical Impedance Spectroscopy on Platinum Microelectrodes Integrated in a Microfluidic Chip

Herein, we present a microfluidic device for performing microRNA (miRNA) detection by Electrochemical Impedance Spectroscopy (EIS) on platinum electrodes.miRNAs are noncoding RNAs composed of approximately 19-24 nucleobases; recent research demonstrated their potential as biomarkers for inflammations, cancers, and other diseases diagnosis [1]. Electrochemical biosensors for short nucleic acid detection, compared with other detection techniques, are promising due to low-cost production, fast response, and direct electronic signal transduction.Our biosensor principle is based on the functionalization of capture probes at the electrodes, and successive target recognition via hybridization. For this reason, the immobilization and good alignment of the single-stranded DNA (ssDNA) probes at the electrode is the first delicate step, and it is necessary for facilitating the hybridization with complementary targets. Previous studies demonstrated a strong affinity between Pt surfaces and oligonucleotide backbones [2]; as a result, providing suitable probes orientation on Pt electrodes is challenging.The EIS provides high sensitivity for characterizing surface modifications. It consists of measuring the equivalent impedance of the electrochemical system by applying a small AC voltage to the electrodes. The well-known Randles circuit represents the equivalent circuit of an electrode/electrolyte system, and the resulting equivalent impedance is translated into the formula expressed in Figure A [3]. The solution resistance element (Rs ) depends on the electrolyte conductivity. The charge transfer resistance (Rct ) is related to the electroactive electrode surface. The double-layer capacitive component (Qdl ) is the electrical translation of the solution-free ions arranging form when a potential is applied to the electrodes; it represents a constant phase element, which depends on the exponent α related to the surface uniformity. Finally, we have the diffusion-convection complex impedance (Zdc ).The microfluidic chip is composed of a glass substrate and a polydimethylsiloxane cover which contains a 60 µm heigh channel pattern. After a photolithography step, we evaporated 10 nm of Titanium as an adhesion layer, followed by 100 nm of platinum for our working and counter electrodes (WE and CE) on the glass substrate. The surface area of the WE is 90·10-6cm2, 60 times bigger than the CE.We successfully completed an electrochemical pretreatment of the Pt electrodes in microfluidics with Potassium hydroxide (100mM), performing 10 cycles of cyclic voltammetry between -0.2 V and -1.2 V.The EIS measurements employ a 20 mmol/L [Fe(III)(CN)6] 3- / [Fe(II)(CN)6] 4- electrolyte under a 0.5 µL/s flow. The applied AC voltage amplitude is 10 mV, and its frequency is swept down from 1 MHz to 100 mHz.In this study, we compare the immobilization of ssDNA with and without the introduction of MCH (Figure B). Our 21-base thiol-labeled ssDNA has a concentration of 10-6 mol/L. The functionalization is held for 1 hour and 30 minutes in static for both cases, but, in the second case, 10-5 mol/L of MCH is introduced before the probes for 30 minutes. We performed a static hybridization for 30 min of 10-14, 10-10, and 10-6 mol/L complementary target concentrations.We collected the data for bare electrodes, probes-functionalized electrodes, and after the introduction of the targets at the three concentrations in the case with and without MCH, and we fitted with the equation in Figure 1A. Figure C represents the electrode fractional coverage (θ) with respect to the concentration of the targets, in the case without (black line), and with MCH (red line). It is possible to observe that the θ parameter increases at each target concentration introduction in the case with MCH. In fact, the DNA-monolayer is negatively charged, and it attenuates the electrode/electrolyte redox exchange; consequently, the charge transfer resistance significantly increases. On the other hand, the fractional coverage in the case without MCH introduction is stable next to zero. We suppose this is because the ssDNAs are not well oriented (as depicted in Figure B-left ); therefore, the hybridization does not occur.In this study, we presented our microfluidic chip and a new protocol for DNA probes functionalization on Pt electrodes. In particular, we succeeded in providing suitable ssDNAs orientation that avoids DNA bases-Pt interactions. Current studies include coupling our electrochemical biosensor with a microcalorimeter to increase the specificity of the detector and testing in biological samples.The authors would like to thank the DIMELEC project for funding and RENATECH clean room facilities at C2N, Palaiseau, France.[1] G. A. Calin and C. M. Croce, Nat. Rev. Cancer, vol. 6, no. 11, pp. 857-866, 2006.[2] W. Zhou, et al. Chem. Commun., vol. 51, pp. 12084-12087, 2015.[3] C. Poujouly, et al. Electrochemistry Communications, vol. 137, 107262, 2022. Figure 1

(Invited) Numerical Simulation of Ohmic Impedance

Impedance spectroscopy measurements are often confounded by high-frequency phenomena associated with frequency-dependent ohmic resistance. Newman introduced the concept of frequency dispersion to account for the effect of the disk electrode geometry on the impedance response [1]. The phenomenon described by Newman in terms of frequency-dependent capacitance and ohmic resistance may be considered as an ohmic impedance, a transfer function associated with the resistance of the electrolyte to passage of current under the influence of geometry-induced (and frequency-dependent) non-uniform current and potential distributions [2].Two kinds of models are described in the presentation. Finite-element models account for the influence of geometry on the impedance response for a disk electrode. These models demonstrate the ohmic impedance. The second model is an interpretation model used to extract properties from impedance data. For most cases, data are truncated to avoid being confounded by ohmic impedance. On rare instances, the ohmic impedance may be extracted by regression to data.Gharbi et al. [3] suggested that the ohmic impedance follows the form of the Havriliak-Negami equation. The Havriliak-Negami equation was found to provide a good fit to the ohmic impedance calculated for different electrode geometries, including interdigitated electrodes [4] as well as disk electrodes [3].The ohmic impedance was obtained by Levenberg-Marquardt regression of a process model that accounted for the ohmic impedance [5]. The experiments were performed using ferri/ferrocyanide redox species (10 mM each) in a 0.5 M KCl solution. The working electrode consisted of a 5-mm-diameter Au disk rotating at 800 rpm. A Pt gauze (4 cm2) was used as the counterelectrode, a saturated Ag/AgCl electrode was used as a reference electrode, and the temperature of double-walled electrochemical cell was held at 25 ±0.1°C.The process model was expressed in terms of an ohmic impedance and an expression that accounted for the influence of a local constant-phase element on the faradaic reaction and the convective diffusion impedance, expressed in terms of a series expansion following the work of Tribollet and Newman [6]. Regressions were weighted by the experimentally determined error structure of the data, and the resulting parameters characteristic of the ohmic impedance were in excellent agreement with numerical simulations.References J. S. Newman, J. Electrochem. Soc., 117 (1970), 198.V. Huang, V. Vivier, M. E. Orazem, N. Pébère, and B. Tribollet, J. Electrochem. Soc., 154 (2007), C81-C88.O. Gharbi, A. Dizon, M. E. Orazem, M. T.T. Tran, B. Tribollet, and V. Vivier, Electrochim. Acta, 320 (2019), 134609.A. Dizon and M. E. Orazem, Electrochim. Acta, 337 (2019), 135000.W. Watson and M. E. Orazem, EIS: Measurement Model Program, ECSArXiv, 2020, https://ecsarxiv.org/kze9x/.B. Tribollet and J. S. Newman, J. Electrochem. Soc., 130 (1983), 2016.

Possibilities of Checking Water Content in Porous Geopolymer Materials Using Impedance Spectroscopy Methods.

The porous geopolymer has been tested for its content of water using impedance methods. The pores of the material were filled with distilled water using a desiccator and a vacuum pump. An analysis of differential scanning calorimetry (DSC) was carried out in the next step to check the content of water, porosity and approximate value of specific heat of the geopolymer. Additionally, mercury porosimeter has been used for checking the porosity. The geopolymer material characterized in this way was subjected to impedance tests aimed at developing a quick method for assessing the water content in the material. Impedance measurements have been realized on an electrochemical workstation applying a 50 mV non-destructive amplitude of the potential and a frequency range of 1 Hz to 100 kHz. Change in the module of impedance and the phase shift angle were measured while the material was dried out. Significant differences were observed. The obtained graphs were simulated using a schematic model consisting of constant phase elements (CPEs) and a resistor (R). These values showed mechanisms of charge conduction. A simple method for assessing the water content of a porous geopolymer has been proposed in this paper. The real and imaginary impedance values were shown in Nyquist graphs. These graphs have characteristic maxima that move according to a linear equation with decreasing water content. Changes in Nyqiust charts are clearly visible even with small changes in the water content of the material and can be very useful for assessing it.

CATHODIC EVOLUTION OF HYDROGEN ON IRON DISILICIDE IN ALKALINE ELECTROLYTE

The kinetics and mechanism of hydrogen evolution on the FeSi2 electrode in 0.25-1.0 M NaOH solutions have been studied by polarisation and impedance measurements. The cathodic polarisation curves of iron disilicide in the studied solutions are characterized by a Tafel region with constants α and β equal to (-0.78)-(-0.72) and (-0.133)-(-0.128) V, respectively. The impedance spectra of FeSi2 at the potentials of the Tafel region represent a capacitive semicircle with a displaced centre, which corresponds to an asymmetric maximum in the graph of phase angle dependence on the logarithm of the alternating current frequency; the magnitude of the electrode impedance in all solutions changes in accordance with the course of the polarization curves. To describe the hydrogen evolution reaction on iron disilicide, an equivalent electrical circuit was used, the Faraday impedance of which consists of series-connected charge-transfer resistances and a parallel circuit responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material; the circuit also includes the electrolyte resistance and the double-layer capacitance impedance, which is modelled by a constant phase element. It is shown that the results of polarization and impedance measurements for the FeSi2 electrode are in satisfactory agreement with the discharge-electrochemical desorption mechanism, in which both stages are irreversible and have unequal transfer coefficients; for adsorbed atomic hydrogen, the Langmuir adsorption isotherm is satisfied; simultaneously with the reaction of hydrogen evolution, the reaction of hydrogen absorption by the electrode material proceeds with diffusion control. It has been found that iron disilicide in an alkaline electrolyte is characterised by the low overvoltage of hydrogen evolution, and it is a promising electrode material for the electrolytic production of hydrogen.

A Unified Description of the Electrical Properties with Complex Dynamical Patterns in Metal Halide Perovskite Photovoltaics

One of the most promising emerging photovoltaic technologies is represented by perovskite materials essentially due to their outstanding performance. However, the complex fundamental understanding of relevant device physics is challenging, making it harder to obtain correlations with efficiency and long-term stability, and thus definitely transforming the landscape of solar energy. In electrical terms, perovskite solar cells often show different types of experimental behaviors at long timescales (light-enhanced capacitance and chemical inductor) in separate voltage domains, but with permanent deviations from the ideal pattern (Cole–Cole relaxation processes, fractional dynamics, and beyond). Here, we reevaluate the dynamical behavior of a photovoltaic perovskite model that leads to the two versions of constant-phase element behavior in the impedance response. Our general theory is, therefore, able to explain naturally the vast majority of results concerning the nonlinear polarization mechanisms of perovskite solar cells, extending the mathematical framework from the perspective of fractional-order electrical circuits. In this context, we discover a novel property that reveals the anomalous electrical coupling of memory effects in photovoltaic perovskites. We hope that this work can provide a useful tool for modeling experts and device physicists belonging to the photovoltaic community, moving forward toward addressing the outstanding challenges in this fast-developing field.

Impedance spectroscopy technique for estimating the oxidation of the PyC interphase layer in a SiCf/SiC ceramic matrix composite

ABSTRACT A new technique using impedance spectroscopy was developed to estimate the oxidation kinetics of the pyrolytic carbon interphase layer in SiCf/SiC ceramic matrix composites. The AC impedance Nyquist plot showed two semicircles that were curve-fitted using an equivalent circuit with two constant-phase element components. The analysis results revealed that the capacitance in the low-frequency region decreased with increasing oxidation time, whereas that in the high-frequency region remained relatively constant. This change in the capacitance in the low-frequency region was associated with the thickness of the oxidized SiO2 layer. This study might make a significant contribution to the literature, which has mostly focused on the characterization of ceramic matrix composites through measurements of mechanical properties. The limitations and potential applications of the developed method were also elucidated.

Electrode potential, inflammatory solution chemistry and temperature alter Ti-6Al-4V oxide film properties

Post implantation, a thin TiO2 film protects Ti-6Al-4V in vivo. Mechanically and chemically destructive conditions may disrupt this oxide film and promote corrosion at the device interface. While tribocorrosion has been explored in vitro, pre-clinical tests fail to fully reproduce the damage documented on retrievals. A gap persists in our fundamental knowledge of the oxide film and its response to adverse electrochemical events. In this study, we first characterized the TiO2 oxide film structure after inducing β phase selective dissolution. Next, we used electrochemical impedance spectroscopy and Mott-Schottky analysis to investigate the oxide film on freshly prepared surfaces following negative potential excursions. We systematically increased electrode potential from -1 V vs. Ag/AgCl in 0.1 V steps to +0.5 V. Various H2O2 concentrations (0.1 M to 0.001 M) in phosphate buffered saline and temperatures ranging from 24 °C to 55 °C were investigated. Atomic force microscopy showed morphological changes to oxide domes over the α phase following β phase selective dissolution. Below the Ti-6Al-4V open circuit potential (ca. -0.3 V), we identified systematic variations in polarization resistance (Rp) and capacitance (C) with potential, solution chemistry, and temperature. The combined effect of cathodic activation and H2O2 solution concentration synergistically and systematically decreased Rp by orders of magnitude (p = 0.000). Increased solution temperatures decreased Rp (p = 0.000). At high concentrations of ROS (0.1 M), we documented changes in constant phase element capacitance, from n-type to p-type. Finally, we developed empirical equations to predict Rp for a given concentration, temperature, and potential. In totality, these experiments help to further elucidate the complex interactions at the oxide-biology interface in vivo and provide guidance for in vitro testing methods development.

State of charge estimation for lithium-ion batteries based on a novel complex-order model

The accuracy of the battery model is decisive in model-based state of charge (SOC) estimation. In this paper, complex-order derivatives (CDs) are applied in the scope of battery modeling, parameter identification, and SOC estimation. Firstly, a novel complex-order equivalent circuit model (Co-ECM) for lithium-ion batteries, which considers an innovative complex-order constant phase element, is proposed. Secondly, the structure characteristics of the Co-ECM are analyzed, and a complex-order particle swarm optimization algorithm is developed to identify the Co-ECM parameters. Finally, a novel complex-order unscented Kalman filter is designed to estimate the battery SOC, while CDs capture the system past behavior and tackle the nonlinearities of the constant phase element. Also, the proposed Co-ECM is compared with two other alternatives (i.e., integer-order and fractional-order ECM) based on data from two battery test cycles at different temperatures. The results show that the new Co-ECM leads to SOC estimation accuracy higher than the traditional models over a wide range of temperature (0∘C, 25∘C and 45∘C), with root-mean-squared error (RMSE) and mean absolute error (MAE) less than 0.47% and 0.41%, respectively. Moreover, experiments with data polluted with artificial noise revealed that the proposed model has superior robustness against noisy information. The new Co-ECM is, thus, shown to be a prime option for battery SOC estimation.

Parameter Estimation of the Single-Dispersion Fractional Cole-Impedance Model With the Embedded Hardware

Bioimpedance modeling with equivalent electrical circuits has an important role in various biomedical applications, as it facilitates understanding of underlying physical and electrochemical processes in applications such as body composition measurements and assessment of clinical conditions. However, estimation of model parameter values is not a straightforward task, especially when complex circuits with fractional-order components (e.g. constant phase elements) are used. In this paper, we propose a low-complexity method for parameter estimation of the Cole-impedance model suitable for low-cost embedded hardware (e.g. 8-bit microcontrollers). Our approach uses only the measured real and imaginary impedance, without any specific software package/toolbox, or initial values provided by the user. The proposed method was validated with synthetic (noiseless and noisy) data and experimental right-side, hand-to-foot bioimpedance data from a healthy adult participant. Moreover, the proposed method was compared in terms of accuracy with the recently published relevant work and commercial Electrical Impedance Spectroscopy software (Bioimp 2.3.4). The performance evaluation in terms of complexity (suitable for deployment for the microcontroller-based platform with 256 kB of RAM and 16 MHz clock speed), execution time (18 seconds for dataset with 256 points) and cost (<25 USD) confirms the proposed method in regards to reliable bioimpedance processing using embedded hardware.

Electrochemical performances investigation of bismuth selenide Bi2Se3 layer for capacitors application

Bismuth selenide (Bi2Se3) layers have proved useful as electrode materials for capacitors. This material was prepared via electrodeposition method with the different deposition time and characterized by X-ray diffraction, Scanning electron microscopy, and Energy dispersive X-ray spectroscopy techniques. It is found that the films of Bi2Se3 provoke the formation of a biphasic, orthorhombic and rhombohedral crystal structure, with uniform spherical particles. Furthermore, the electrochemical properties of Bi2Se3 were investigated using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in 1 M HNO3 aqueous electrolyte. Galvanostatic charge-discharge measurements deliver a specific capacitance of 49.7 mF g−1 which leads to a specific energy density of 0.0034 Wh kg−1 and specific power of up to 5 kW kg−1 at a current of 0.01 A g−1. The electrochemical impedance data were fitted with an equivalent circuit containing a constant phase element and fitted parameters were calculated.

Fractional model of the chemical inductor

A multitude of materials and processes of a different nature frequently exhibit, in addition to the classical capacitive arcs, inductive loops in the complex impedance plane. It is a stable and physically robust response originated, from a mathematical perspective, by the introduction of a capacitive coupling in the slow relaxation variable. Nevertheless, the dynamical behavior of such systems shows, in reality, pronounced experimental deviations from the ideal inductive behavior. For this reason, the scientific community in general claims for the development of a novel theory that helps to phenomenologically interpret this pattern change, also encompassing the associated inherent physical complexity that capitalizes on the vast majority of real-world processes. Here, we present a generalization of the classical fast-slow models to naturally explain the anomalous dynamics observed experimentally in different types of measurement techniques, such as the inductance dispersion in impedance, the fractional relaxation processes with negative spike components in the transient responses, and the inverted current-voltage hysteresis. From numerical simulations, we analyze in detail the crossover dynamics from capacitive to inductive properties from the perspective of the constant phase element. Our work devises a useful theoretical framework that explains, in frequency and time domain, the coexistence of dispersive features and the transformation of the electrical behavior in terms of an anomalous bifractional crossover. Finally, we show the dominant role of the fractional-order dynamics in the appearance of inverted hysteresis commonly found in current-voltage curves. Although in literature, everything looks, in a certain manner, simple, the reality is that many real-world materials exhibit an intricate and complex nature that leads to anomalous processes evidenced by dispersive dynamics observed through different measurement techniques. This change of pattern analyzed here is appealing as a mathematical tool to interpret the physical phenomena of many familiar systems.

Use of reduced-voltage EIS to establish a relation between oxygen concentration and EIS responses of large commercial PEM fuel cell modules

This paper employs equivalent circuit analysis of electrochemical impedance spectra (EIS) signatures of commercial proton exchange membrane fuel cell stacks (PEMFC) to establish a relation between oxygen concentration and EIS response within individual cells of the stack. This paper is part of an ongoing effort to use EIS for detecting and quantifying hydrogen crossover to understand and reduce hydrogen cathode exhaust emissions. Selected results from different sets of experiments performed on Ballard water-cooled and air-cooled PEMFC stacks are presented. A novel reduced-voltage EIS system with the ability to perform impedance measurements over different cell counts is employed to record EIS scans of these stacks. In the first set of experiments, hydrogen was injected into the cathode side of a 30 kW 150+-cell water-cooled module at various rates to emulate the phenomenon of hydrogen crossover at different levels. In the second set of experiments, nitrogen was injected into a target single-cell in an air-cooled stack with over 50 cells (50+-cell) to dilute the cathode available oxygen, and the impedance was measured over various numbers of cells spanning around this target cell. A novel equivalent circuit model with resistors, constant phase elements (CPEs), and a linear finite Warburg parameter was used to study the EIS data via an optimization-based fitting approach in python. Results of these experiments have shown there is a proportional relationship between the Warburg parameter (in the equivalent circuit model used) and hydrogen crossover (at nominal idle and low-current air flows), and that this Warburg parameter increases significantly with reduced cathode air flows. Also, it is concluded that this relationship can be further used, along with decomposition of the EIS scan of a stack into different cell-level scans, to estimate the number of large-leaky cells as well as the total hydrogen crossover rate.

Fractional‐order LC filter modeling, implementation, and analysis for distributed power generation system

SummaryThis paper proposes a comprehensive mathematical modeling and analysis considering fractional‐order LC filters (FOLCF) in the utility grid‐connected mode (UGCM) and the standalone mode (SM) of operation for the distributed power generation system. The fractional‐order behavior of LC filter elements helps to more properly depict a practical inductor or capacitor than the integer‐order LC filters (IOLCF) in the distributed power generation system. The fractional‐order model of UGCM and SM is obtained in the synchronously rotating reference frame using coordinate transformation. A detailed stability and time domain analysis is performed on the developed FO UGCM and SM mathematical models. The stability of fractional‐order LC filters increases for orders less than 1, based on the performance evaluation of the FO and IO mathematical models for UGCM and SM with the corresponding designed controller gains. The FOLCFs are approximated using the constant phase element method, which gives a compact and exact approximation of the fractional‐order inductor and capacitor elements. The implementation of FOLCF with UGCM and SM operations verifies the effectiveness of the proposed model in real‐time simulation. The results show the FOLCF model provides better dynamic tracking and disturbance rejection response than the IOLCF model. Hence, the FOLCF model imparts immunity against local load disturbances to regulate the point of common coupling voltage and frequency in standalone mode. Furthermore, a significant improvement in % total harmonic distortion is also observed in grid current and load voltage.

Impedance spectroscopy of amorphous/crystalline silicon heterojunction solar cells under dark and illumination

In this article, the electronic properties of a-Si:H/c-Si heterojunction (SHJ) solar cells are analyzed by performing impedance spectroscopy (IS) characterization in the dark and under controlled illuminations. Various dynamic electrical processes occurring at different time scales, ranging from microseconds to milliseconds, are observed mainly in the operating regime of the device. Several distinct characteristics are observed: a) time constant distribution characteristic of the disordered junction, b) typical bias voltage and illumination intensity dependence of the recombination time constant, and c) an additional time constant indicative of a fast process, which appears only under illumination. The impedance spectra of the SHJ cell are best modelled by including a dispersion element, the constant phase element (CPE), in place of a pure capacitor, in its small signal electrical equivalent circuit (EEC), aside from the pure resistive and capacitive elements arranged in a simple configuration. The CPE behavior is assigned to the complex small signal response originating from the distribution of trap levels in the disordered p+-a-Si:H/n-Si heterojunction. Under illumination, a distinct dynamic process is observed compared to the dark condition in the impedance spectra of the device. The variation of the dispersion parameter, resistances, capacitance, and time constants with external stimuli is discussed. In particular, the variation of the recombination time constant with bias is remarkable under different illumination intensities due to the change in the quasi-fermi levels splitting.

Temporal Aspects of Corrosion Inhibition on Copper, Silver, and Copper-Silver Alloys: An Electrochemical Impedance Spectroscopy Study

Electrochemical impedance spectroscopy (EIS) was utilized to delve into the corrosion inhibition of eutectic Cu-Ag alloy and its components (Cu and Ag) in an aqueous, aerated 0.1 M KNO3 solution. This alloy plays a major role in the water cooling of central processing units in data storage centers. Two organic inhibitors, namely, 1,2,3-benzotriazole (BTA) and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), were utilized in this study. The corrosion inhibition slowly evolved over time as diagnosed by an increase in the charge transfer impedance and the gradual tendency of the Nyquist profiles to arc toward the real axis. This trend was attributed to the gradual formation of organometallic passivation layers. The EIS data underlined the specific affinity of BTA and DMTD toward the Cu and Ag surfaces, respectively. A transition of the double-layer equivalent circuit element from ideal capacitance to a constant phase element was observed for the alloy compared to the pure metals. This was attributed to the heterogeneity induced by Cu-rich and Ag-rich phases in the alloy and by the formed oxides/protective film on the alloy surface. The EIS study demonstrated that both BTA and DMTD can provide sufficient corrosion inhibition to Cu-60Ag alloy with DMTD being significantly more effective.

Equivalent circuits studied by means of electrochemical tests employing different inoculum and simultaneous treatment during bioelectricity production in a single chamber-microbial fuel cell

Microbial fuel cells (MFC) have attracted the attention of scientists due to their capacity to improve electricity production and to employ wastewater as substrate. This duality results in a source of clean energy and degradation of the organic matter. The use of catalysts such as platinum make the implementation of these technologies difficult, therefore, it is a challenge to find economically feasible options and strategies carry out studies. Stream sediments (SS) and anaerobic granular sludge (AGS) were compared in a single chamber-MFC. Reactors constructed with Plexiglas contained carbon cloth cathode treated with polystyrene, graphite felt anode, and acetate as substrates. The voltage was measured with a digital multimeter, whereas power density and Coulombic efficiency were calculated based on Ohm’s law. The electrochemistry impedance spectroscopy analysis was determined with an equivalent circuit model resistances. AGS-MFC produced 1.35 mW/m2 and 30 mA/m2, while SS-MFC produced 1.25 mW/m2 and 20 mA/m2 of power density and current density, respectively. AGS-MFC showed a 10% greater Coulombic efficiency compared to the one obtained from the SS-MFC. In this research, the effect of the inoculum on power density in an MFC was evaluated with the objective of finding sources of microorganisms with better capacities for electricity production and organic matter degradation. The equivalent circuit model showed that AGS-MFC obtained the lowest charge transfer resistance value and the highest constant phase elements values. AGS was the inoculum that showed the best performance in the MFC in terms of voltage and power density.

Photo electrochemical properties of LaCoO3 synthetized by chemical route. Application to orang II photo-oxidation

The perovskite LaCoO3 prepared from nitrates was successfully applied in the oxidation Orange II (OII) under sunlight. The X-ray diffraction (XRD), Scanning Electron Microscopy and electrical conductivity were used for its characterization. The XRD pattern showed that the single phase is completed at 850 °C and the oxide crystallizes in a distorted structure. The optical gap (1.35 eV), determined from the diffuse reflectance, is due to the crystal field splitting of Co3+ octahedrally bonded with a low spin configuration (3d6). A hole mobility of 10−2 cm2 V−1 s−1 and an activation energy of 0.11 eV were deduced from the conductivity measurement. LaCoO3 attractive with regard to toxicity concern exhibits a chemical inertness at neutral pH (Na2SO4, 0.1 M) with an exchange current density of 40 μA cm−2. The variation of the capacitance (C−2) with the potential (E) is characteristic of p type comportment with a flat band potential of 0.30 VSCE. The EIS date showed an arc due to the resistance of the bulk material (1153 kΩ cm2) whose center center is below the real axis (-16°) assigneed to a constant phase element (CPE). The conduction band (-0.94 VSCE), deriving from Co3+: 3d wave function, allows the generation of O2•− species and as application, the oxide was positively tested for the mineralization of OII upon sunlight. The hetero-system p-LaCoO3/n-ZnO improves significantly the photo catalytic performance -activity, due to the facile electronic transfer with an oxidation of 86%. The oxidation kinetic obeys a first order model with a half life of 23 min.

An approach to unify capacitance measurements of electric double layer capacitors using sinusoidal potential scan

Measuring supercapacitor capacitance is essential to understanding their electrical characteristics. However, different techniques can provide significantly different capacitance values. This discrepancy makes it difficult to compare results and communicate new research findings, hindering the progress of supercapacitor technology, particularly electric double layer capacitors (EDLCs). Voltammetry techniques often assume an ideal capacitor, while electrochemical impedance spectroscopy (EIS) recognizes the need to model the non-ideal electrode behavior with a constant phase element (CPE). Through comparison with the responses of two commercial EDLCs, this study confirms that the time domain responses of EDLCs should be modeled with CPE rather than a pure capacitor. The derived equations are then used to examine the effects of experimental conditions and the CPE exponent on capacitance measurements in cyclic voltammetry (CV). The study shows that estimated capacitances are affected by several experimental conditions, not only the scan rate, highlighting the need for an alternative approach to unify the capacitance measured using different analytical methods and measuring techniques. Therefore, this study proposes an alternative approach to estimate the capacitance of a CPE using a sinusoidal potential scan in voltammetric measurements. This approach not only equalizes the capacitance measured using different analytical methods and measuring techniques but also significantly reduces the number of experimental parameters affecting the calculated capacitance to just the frequency (or scan rate). The findings of this study offer valuable insights into the estimation of capacitance via various methods and have potential implications for improving the performance of electrochemical devices, particularly EDLCs, in the pursuit of a clean energy future.

Electrical Transport Mechanisms in Graphene Nanoplatelet Doped Polydimethylsiloxane and Application to Ultrasensitive Temperature Sensors.

The temperature effect on electronic transport mechanisms in graphene nanoplatelet (GNP) doped polydimethylsiloxane (PDMS) for temperature sensing applications has been investigated under electrical impedance spectroscopy (EIS) analysis. AC measurements showed a very prevalent frequency-dependent behavior in low filled nanocomposites due to the lower charge density. In fact, 4 wt % GNP samples showed a nonideal capacitive behavior due to scattering effects. Therefore, the standard RC-LRC circuit varies with the substitution of capacitive elements by CPEs, where a CPE is a constant phase element which denotes energy dissipation. In this regard, the temperature promotes a prevalence of scattering effects, with an increase of resistance and inductance and a decrease of capacitance values in both RC (intrinsic and contact mechanisms) and LRC (tunneling mechanisms) elements and, even, a change from ideal to nonideal capacitive behavior as in the case of 6 wt % GNP samples. In this way, a deeper understanding of electronic mechanisms depending on GNP content and temperature is achieved in a very intuitive way. Finally, a proof-of-concept carried out as temperature sensors showed a huge sensitivity (from 0.05 to 11.7 °C-1) in comparison to most of the consulted studies (below 0.01 °C-1), proving, thus, excellent capabilities never seen before for this type of application.

Temperature-driven complex dielectric and polaron-hopping mediated electrical conduction in aurivillius Gd2MoO6

In this work, aurivillius gadolinium molybdate (Gd2MoO6) was synthesized by the conventional solid-state route which was accompanied by cutting-edge characterization i.e., structural, and electrical, to give insight into the material characteristics required for possible high-temperature applications. The single-phase crystalline nature with monoclinic symmetry (C2/c, Space group-15) of Gd2MoO6 was confirmed by the X-ray diffraction (XRD) pattern. The average particle size was obtained to be ∼0.495 µm. The electrical conductivity and dielectric properties of a Gd2MoO6 plate capacitor were investigated in the frequency range between 10 Hz and 1 MHz and temperature from 473 to 773 K. A high dielectric constant (ε') of ∼3272 and low dielectric loss (δ) of ∼200 was observed at the low frequency and high-temperature regions, respectively. The Maxwell–Wagner interfacial polarization was found to be responsible for the decrease of the dielectric constant with increasing frequency. The behavior with the temperature of the frequency exponent (n) from the fitted conductivity spectra by Jonscher power law corresponds to the non-overlapping small polaron tunneling model between 473–673 K and correlated barrier hopping model at/over 673 K. The non-exponential Kohlrausch Williams-Watts function was introduced to fit the imaginary modulus (M′′) spectra and the activation energy was obtained to be 0.81 eV for grain and 0.94 eV for grain boundary conduction. The Nyquist plots(Z′vs.Z′′) differentiate the grain and grain boundary contribution and were fitted with the combinations of resistance (R), capacitance (C), and constant phase element (Q) in an equivalent circuit model(RC)(RCQ). Typical negative temperature coefficient of resistance behaviors of Gd2MoO6 suggest its possible application as thermistors in modern electronics circuits.